13] Flow birefringence

Self-assembly of particles—The regulatory role of particle flexibility

Assuming an irreversible, random, end-to-end aggregation of a small percentage of potato X virus in tobacco sap, the flow birefringence parameters of such polydisperse systems have been calculated. The extinction angles χ were evaluated for different values of the ratio G/θ1(G gradient θ1, rotary diffusion constant of non-aggregated virus) for preparations containing between 0 and 15% by weight of aggregated material. A particle length of 6200 Å for the non-aggregated virus particle was derived and an amount of 13–15% aggregated material was estimated.A partially purified and fractionated preparation of potato X virus was also investigated and an average particle length of 5400 Å was derived. Because of the possible contribution of small fragments, this length was taken as the lower limit.The flow birefringence – gradient curve indicated that the potato X virus behaves like a rigid particle. No evidence of flexibility was obtained from extinction angle – gradient measurements in the range 0.1–0 M phosphate buffer concentrations at pH 7.2.

The flow birefringence and extinction angle over a velocity gradient range of approximately 5–100 sec−1, and the zero shear‐viscosity have been obtained from human umbilical cord hyaluronic acid at concentrations of 0.25, 0.125 and 0.0625%, and pHs 6.0, 6.5, 7.0, 7.5, 8.0, and 8.5 and constant ionic strength 0.1. The data indicate a large change in optical anisotropy as a function of pH, with most of the transition in the pH range 7.0–7.5, i.e., across the physiological range. The sign of the anisotropy changes between pH 8.0 and 8.5. These results, together with changes in the extinction angle and intrinsic viscosity as a function of pH, suggest a pH‐dependent structural change in the system. Due to the abruptness of the transition, as evidenced by the intrinsic viscosity and flow birefringence, it is probable that the structural transition is cooperative. If the data are interpreted in terms of the Rouse‐Zimm Gaussian subchain theory, a modification of the model in terms of the Haller‐Cerf concept of internal viscosity is required. Thus, the demonstrated properties of hyaluronate solutions indicate a system with memory of stress. Due to the presence of large concentration effects discernible in the extinction angle measurements, hyaluronic acid probably exists as a network in solution. The results are discussed with respect to the mechanoelectrical transducing properties of hyaluronates and stress‐dependent changes in ORD already reported.

Extinction angles, intrinsic viscosities, and molecular weights of polystyrene in solution

Particle size, shape and mineralogy are considered as primary characteristics of sand and sandstone. Several techniques have been developed for the particle size and shape analysis of unconsolidated sands. However, few of these techniques can be used for sandstones. Most particle size measurement techniques provide a spherical equivalent of the particle size and neglect the particle shape. Although several techniques have been developed for the particle size and shape analysis of the unconsolidated sands, these techniques could not be used for the size and shape variation analysis of consolidated or semi-consolidated sandstone. Recently, X-ray micro CT scanning technique has been used for the evaluation of petrophysical properties of sandstones. This paper presents a workflow for the measurement of particle size and shape of sandstones. This research utilized X-ray micro CT scans for 2-dimensional particle shape measurements including Sphericity, Convexity, Aspect Ratio and Feret diameters. The methodology presented in this paper is the first step toward assessing the particle shape and size variation of sandstones for use in such applications as sand control design. Image-J, an Open-source software, was used to process and filter the X-ray raw images. A new tool was developed to measure the shape factors (i.e. Sphericity, Aspect Ratio and Convexity) and size variations. A series of images from different sandstones were analyzed and compared to their lab measurements. The image calculated porosity and permeability showed some degree of deviation from the lab measured porosity and permeabilities. This paper presents a new workflow to measure the particle size and shape for the sand control design in sandstone reservoirs. With a larger database it is possible to develop a correlation to calculate rock properties from image size analysis technique and correct them for the shape variation. The next step will be to measure the 3D size and shape from the image analysis and compare to the shape and size analysis from dynamic image analysis.

We report on the rheo-optical properties of dilute surfactant solutions which exhibit a shear-induced thickening transition. The surfactant investigated is cetyltrimethylammonium tosylate at concentrations around 0.2 wt % in water. By comparing data obtained by rheology and rheo-optics, we first confirm that the thickening transition is associated with the transformation of the initially isotropic micellar liquid into a birefringent and strongly aligned phase. In both experiments, the transition occurs at the same critical shear rate, denoted γ̇c. Using a new treatment for the analysis of the rheo-optical data, we have been able to determine the birefringence Δn and extinction angle χ at steady state, but also as a function of the time and of the spatial coordinate in the 1 mm gap of a Couette-type shearing cell (with a spatial resolution of 15 μm). Starting from a solution in a quiescent state and applying steady shear, we provide an accurate description of the kinetics of formation of the shear-induced and viscous phase. At steady state, we observe strong variations of the flow birefringence Δn as a function of the spatial coordinates within the gap, as well as a failure of the stress-optical law. The extinction angle χ is then close to 0°, independent of the shear rate and of the spatial coordinates. The flow birefringence also exhibits rapid fluctuations around the average profiles, on a length scale comprised between 50 and 100 μm. These fluctuations are interpreted as shear bands of enhanced and reduced birefringence, a result which suggests a strongly inhomogeneous and instable shear flow in the shear-induced phase.

Extinction angles, flow birefringence, and intrinsic viscosities are compared for linear, bihelical DNAs from viral and other sources that span a range in molecular weight from ∼105 to 1.3 × 108. This range effectively spans the region over which transition from rigid‐rod to expanded‐coil hydrodynamic property behavior occurs. All DNAs are in identical, phosphate–EDTA, neutral‐pH buffers, 0.1M in NaCl. The extinction angle is a hydrodynamic property only and is thus particularly sensitive to effects of kinetic chain rigidity or internal viscosity. Our extinction angle results cannot be interpreted by any simple, single‐function theoretical expression. Rather, they must be divided into distinct high‐ and low‐molecular‐weight domains. The low‐molecular‐weight region is typical of rigid‐particle opticohydrodynamic property behaviour characterized primarily by particle orientation. The high‐molecular‐weight domain shows evidence for a finite internal viscosity effect, however, which can be interpreted as very nearly Kuhnian using Cerf's amplification of the Gaussian subchain model to include internal viscosity. It is found that the high‐molecular‐weight, monodisperse viral DNAs from T7, T5, and T2 bacteriophage show an internal viscosity contribution to the limiting extinction angle–shear rate ratio of ∼3 × 10−3 s. An effect of this magnitude may be marginally important in interpreting extinction angle and certain other hydrodynamic property data for high‐molecular‐weight DNA systems. Internal viscosity effects do not appear to be manifest in the ratio of flow birefringence to intrinsic viscosity, however, and the persistence length of the high‐molecular‐weight DNAs is found to be independent of molecular weight to within estimated experimental uncertainty.

The optical and hydrodynamic properties of T2 bacteriophage DNA have been determined by steady‐state flow birefringence and viscosity in glycerol–aqueous buffer solvents at 25°C. Flow birefringence and extinction angle data were obtained over a velocity gradient range of 0.1 to 5 sec−1 and at concentrations from 3 to 55 μg/ml in solvents containing approximately 30, 42, and 48 vol‐% glycerol. Large optical backgrounds were observed in the mixed solvent flow birefringence studies which presented special experimental difficulties; these are described and their effect upon the flow birefringence data are discussed. The data on extinction angle provide no evidence for an internal viscosity effect on the stationary‐state hydrodynamic properties of high molecular weight DNA over a range of solvent viscosity from 0.9 to 4.6 cP. Both the optical and hydrodynamic properties under present conditions of measurement appear to be self‐consistent in terms of the values for these quantities in neutral aqueous buffer solution. Interpretation of the birefringence is complicated by uncertainties inherent in calculating the form anisotropy of DNA in non‐aqueous solvents, but the data imply no large changes in helical structure with increasing glycerol concentration. Both intact and slightly degraded DNA samples were investigated, and no significant polydispersity effects were observed under the experimental conditions described.

The extrapolated values of the sedimentation constants of four polystyrene fractions in CHCl3, toluene and MEK were used, in conjunction with osmotic molecular weights and viscosity measurements, to calculate according to the Kirkwood‐Riseman theory the two fundamental molecular parameters b and ζ. Since the same parameters determine the translatory and rotatory diffusion constants, the latter could be calculated and were compared with experimental data on the same fractions from a concurrent investigation on the flow birefringence, and with translatory diffusion data of closely similar fractions. Finally, if the b and ζ values as obtained with the help of the sedimentation constant were introduced into the equation for the intrinsic viscosity, reasonable values for [η] were obtained, although the agreement was not as good as in the case of the diffusion data. It can be concluded that the correlation by means of the basic parameters b and ζ of the four hydrodynamic constants ‐ sedimentation constant, translatory and rotatory diffusion constant and the intrinsic viscosity ‐ is experimentally justifiable, and that the Kirkwood‐Riseman theory offers a satisfactory formalism for the description of these interrelations. There is also a direct correlation between the average chain length from hydro‐dynamic measurements and from light scattering. Earlier reported discrepancies turn out to be only apparent in the light of the present analysis.More specificially it was found that: The sedimentation constants in infinitely dilute solutions are proportional to Mt/2, and that the slope and the intercept of this linear relation vary with the solvent. The changes of shape indicated by the changes in S0 from solvent to solvent yield data from which the average molecular dimensions in the three solvents could be calculated. These dimensions fall in with the corresponding changes in [η].

How to dynamically tune an assembly of anisotropic colloidal particles adsorbed at fluid-fluid interfaces using dipolar capillary interactions is demonstrated. A previously discovered first-order phase transition is exploited and it is shown how to spontaneously turn off these dipolar capillary interactions by exceeding a critical field strength, providing unprecedented control of the bottom-up fabrication of soft materials.

The effect of restriction to a finite number of segments in modeling a flexible macromolecule by a linear Gaussian chain is considered. This model with an internal viscosity included has been used byCerf to develop the behavior of the extinction angle in flow birefringence. The consequences of restriction to a finite number of segments together with variable internal hydrodynamic interaction are determined with respect to the behavior of the extinction angle at low flow gradients and the characteristic chain relaxation times. The theoretical behavior of the extinction angle is shown to depend uniquely on the product of the longest characteristic relaxation time and the flowgradient. The relations between both extinction angle and intrinsic viscosity and the longest relaxation time is dependent upon both number of segments and hydrodynamic interaction. Also the relation given byCerf between gradient dependence of extinction angle and internal viscosity is dependent on both number of segments and hydrodynamic interaction. Results are given for a number of segments ranging from 1 to 1000 and for hydrodynamic interaction ranging from the free draining condition to an extreme nonfree draining condition.

The change in the molecular properties of polyacrylamide and polyoxythylene under the effect of hydrodynamic fields

Flow birefringence and extinction angles have been measured for HMG 14 complexes with nucleosome core particles from chicken erythrocytes under cooperative "tight" binding conditions, and for the uncomplexed core particles used in the preparations. Results are interpreted using optical models for the observed DNA anisotropy, and are compared to recent small angle neutron scattering results. (19) The studies effectively rule out highly distorted DNA conformations and configurations in which DNA ends are unwound and extended. It is concluded that the most likely conformation of the complex is one in which the DNA superhelix is radially increased, either uniformly or bilaterally, with the DNA ends remaining tightly bound to the particle. This conformation does not require large changes in spatial relationships between the DNA ends compared to the uncomplexed core as would accompany, for example, significant unwinding of the ends. However, it may lead to more subtle but possibly highly significant differences in the angles at which the DNA exits the core particle.

The flow birefringence, extinction angles, and shear‐dependent viscosity over a velocity gradient range of approximately 0.1–3 sec−1 have been obtained for T2 bacteriophage DNA at low concentration in neutral aqueous buffer. The data are found to be interpretable and self‐consistent in terms of subchain dynamical theory, including hydrodynamic, interactions and excluded volume, and the parameters characterizing these phenomena are in good agreement with the results of other hydrodynamic experiments and theoretical calculations. No necessity for modification of the subchain model in terms of limited extensibility or internal viscosity is found for high molecular weight DNA at the velocity gradients studied, although the latter cannot be ruled out on the basis of the present data. The Kuhn statistical segment length is determined from the intrinsic optical anisotropy and is estimated as 930 Å. Implications of these findings and their relation to appropriate dynamical models for DNA are discussed.

Rheo-optical investigations on the effect of pentanol on the structure of entangled cetyltrimethylammonium bromide micelles